1. Field of the Invention
The present invention relates to an apparatus for generating a synchronizing signal for applying a radiation to a respiratory moving object.
2. Description of the Related Art
In recent years, computer-assisted diagnosis apparatus such as CT (Computed Tomography) apparatus, CR (Computed Radiography) apparatus, MRI (Magnetic Resonance Imaging) apparatus have widely been used in the medical field.
For imaging the thoracic or abdominal region of an examinee to produce a highly accurate image, it is necessary to take into account the motion of organs in the body of the examinee caused by respiration of the examinee. Though it is customary to ask the examinee to stop its spontaneous breathing during the imaging period, the practice is often burdensome for the examinee. The examinee may possibly be a patient who is unable to stop breathing
The above problems are not limited to the process of imaging examinees. When using radiotherapeutic apparatus, which applies radiation to an affected area of a patient for treatment, it can be difficult to direct radiation accurately if the affected area moves.
Various apparatuses have been proposed for detecting a motion of a respiratory moving object such as an examinee, predicting a position of the respiratory moving object from the detected motion, and applying radiation to the respiratory moving object at a timing based on the detected position. For example, Japanese laid-open patent publication No. 2000-262513 discloses an apparatus for generating X-rays within an exhaling period where the examinee has stable volume fluctuations based on an output signal from a respiratory sensor attached to the examinee, and collecting data from the examinee based on the X-rays applied. According to another apparatus disclosed in Japanese laid-open patent publication No. 7-246245, a synchronizing signal for applying radiation to an examinee is generated based on a signal which is detected by a pressure detector in contact with the body surface of the examinee or an air flow rate detector coupled to the mouth of the examinee.
The conventional apparatuses are capable of applying radiation to the examinee in view of the respiratory action of the examinee. However, the apparatus may not necessarily produce an optimum synchronizing signal because the respiration of the examinee varies widely depending on the age or the respiratory condition of the examinee, and the detected signal changes greatly depending on how the sensor for detecting the respiration is attached to the examinee. In order to generate an optimum synchronizing signal, it is necessary that the examinee or patient be forced to breathe stably. The attachment of the sensor and the adjustment of the sensor output signal must be done by a skilled operator.